Carbon Monoxide Poisoning

What is Carbon Monoxide and How is it Formed?

Carbon monoxide (CO or CO1) is a chemical compound in which a single oxygen atom is bound to a single carbon atom. It is invisible, odorless, and colorless, and it has virtually the same weight as air, which means it won’t sink or rise. It is formed during the incomplete combustion of carbon-based fuels, such as natural gas, propane, oil, gasoline, diesel, and wood, when insufficient air is present. Internal combustion engines and smoldering fires (think cigarettes or BBQ grills) are common sources of CO, as are poorly-maintained “combustion appliances” in the home, such as furnaces, water heaters, and fireplaces. Sources outside your house can also raise the CO level inside your house, such as your car idling in the garage or a gasoline-powered generator running three houses down when your windows are open.

Why is Carbon Monoxide Poisoning so Dangerous?

For humans and most other animals, carbon monoxide reacts with the blood and prevents the blood from carrying oxygen to the brain, heart, and the rest of the body. It does this by bonding with the hemoglobin to form a compound called carboxyhemoglobin (COHb). The bond between CO and hemoglobin is far stronger than the bond between oxygen and hemoglobin, and once COHb is formed, it is difficult to remove. The treatment for carbon monoxide poisoning is to give the victim plenty of oxygen. At atmospheric pressure, it takes 4 – 6 hours to cut the COHb level by half.

Carbon monoxide poisoning can occur at very low levels of CO exposure, albeit slowly. As long as CO is present, it will react with the blood, increasing the level of COHb. Smokers are at particular risk, as CO is present in cigarette smoke, and they often have COHb levels that are several times higher than non-smokers even in clean air. Air pollution can also raise the COHb levels of everyone breathing it. Health authorities have determined that a COHb level of 2% should not be exceeded, and their exposure limits are based on that. Curiously, the UL standard for carbon monoxide detectors is based on alarming when the CO exposure would produce a level of 10% COHb.

How much Carbon Monoxide is Too Much?

There is no single answer that is right for everyone, as each person may have a different tolerance. Young, healthy adults generally have the highest tolerance to CO poisoning, but even then there is a wide range of effects observed. The very young (including the unborn) and the very old are much more at risk of CO poisoning, as are people of any age that have respiratory impairment, such as asthma or emphysema. The following chart shows the effects of rising COHb levels in the blood. Remember as you scan this chart that smokers may already have a COHb level of 10-15% and be suffering from mild CO poisoning.

Symptoms From Increasing % COHb in Blood

What are the Consequences of Carbon Monoxide Poisoning?

As you can see in the above chart, the symptoms of CO poisoning can be quite severe, including death. Unfortunately, the symptoms do not tell the whole story. Most people who are exposed to CO recover fully with no subsequent symptoms, but not everyone. There have been numerous cases where CO poisoning has left the victim permanently disabled, often with brain damage due to insufficient oxygen available. Carbon monoxide poisoning is a tragic situation, but one that is preventable with a working CO detector.